After another La Nina season with again a lot of snow and precipitation in the north central, another active tornado season was expected and so far it has delivered on that promise. However given the La Nina was not as strong and the rebound in the Pacific towards El Nino is a month earlier than last year, the number of storms so far, have been less. Unless major outbreaks occur in late May, it looks like May will fall well short of last May’s 461 tornadoes.

TORNADO TOTALS AND RELATED DEATHS...THROUGH 05/13/2009

NWSSTORMPREDICTIONCENTER NORMAN OK

1048 AM CDT THU MAY 14 2009

...NUMBER OF TORNADOES...NUMBER OFKILLER

TORNADO DEATHSTORNADOES

..2009.. 2008 2007 20063YR3YR3YR

PRELACTACTACTACTAV09 08 07 06 AV09 08 07 06 AV

JAN106842147510721304112

FEB44371475212709 59 220 272 123 05

MAR123-12917014714904 27 11 1403 1077

APR269-189167244200609 38 1630394

MAY165-4612521392846 44 143 203 10415

JUN--294128120181-7002-4001

JUL--93697077-1000-1000

AUG--101758085-0111-0111

SEP--111528482-2011-1011

OCT--21867661-05 02-0301

NOV--1574221-20 104-2032

DEC--46194236-0121-0121

---- ---- ---- ---- ---- -------- -- -- -- -- -- -- -- --

SUM611431691 1098 1103 129721 126 81 67 918 37 26 25 29

PREL = 2009 PRELIMINARY COUNT FROM NWS LOCAL STORM REPORTS.

ACT = ACTUAL TORNADO COUNT BASED ON NWS STORM DATA SUBMISSIONS.

TORNADO-RELATED FATALITY NUMBERS ARE ENTERED WHEN CONFIRMED BY NWS

FORECAST OFFICES.

..CARBIN/PETERS..05/14/2009

The annual summary to date can be found here.The tornadoes so far in 2009 have been in the southeast quadrant of the nation. Climatologically, that is where the season normally begins.

In 2008, the tornadoes when all was said and done, were found in all but 4 of the lower 48 states.

As we move into summer, expect the activity to shift north with the jet stream. The march of the season – climatology of tornadoes normally follows this depiction (source here)

We are above the average for tornadoes for the season to date.

But the number of severe storms to date though is lower than any recent year except 2005.

You can see in 2008 that the daily events peaked in May with the biggest day on the 23rd of May before falling off in summer as El Nino like conditions developed in the eastern Pacific. That is occurring a month earlier this year as noted and perhaps, conditions will quiet down after this week.

The activity was as usual concentrated in what is called tornado alley in the plains, Midwest to the Gulf.

The reason that this region is most vulnerable is that this is where the combination of moisture from the Gulf of Mexico, dry air in mid levels from Mexico, a strong jet with cold air aloft coming out of the Rockies and a boundary between still cool air to the north and the warm humid summer like air in the south all come together.

For more information on tornadoes a couple of good resources are

Storm Prediction Center with daily storm summaries and forecasts and many interesting graphs and charts for recent years like some of those above.